For example: one breeder owned a APHA paint stallion. They said that 90% of his foals (he had quite a few) were paint-marked. Therefore, the paint genes were 'strong', but they couldn't guarantee future offspring would be marked as well.
By using what we know to be common sense in genetics, there are no such things as 'strong' genes. There are only heterozygotes or homozygotes, making either a 50% chance of a gene or 100% chance.
Now, 90% paint-marked foals from a heterozygous stallion may seem like a really large number, but you have to remember that there are other things that could contribute to this.
1. Breeding paint to paint could mean that whatever paint genes the foal inherited could have been from the mother.
2. The stallion is truly homozygous, but some foals were so minimally marked they were recognized as solid. In which case, that foal could produce a crop-out paint and cause a lot of confusion.
Another common mistake among breeders is to assume a horse that has like-parents produce homozygous. For example: a black horse has two black parents. Therefore he is homozygous for black.
This is also not true. If one or both parents were heterozygous for black, then the resulting foal could be heterozygous or homozygous.
All this to say: if you choose to breed and color means something to you, don't believe anything the breeder says about the numbers. Unless you use common sense to figure it out (i.e. look at other offspring and parents), or he has done a genetic color test.
For more reading on the basics, go here: http://michaelashopeandhorses.blogspot.com/2014/11/horse-color-genetics-re-explaining.html
For more reading on crop-out paints and why they happen, go here: http://michaelashopeandhorses.blogspot.com/2014/10/horse-color-genetics-identifying-crop.html
